By David Ward
If you can stay up late enough until it gets dark, and if you dare to brave the swarms of mosquitoes, there are things to see, as always, up in the night sky. The most obvious is the planet Jupiter. Look for it high in the southwest just as it is getting dark.
Jupiter is the largest planet, larger than all the other planets put together. According to recent studies it is also the oldest. Notice that it does not twinkle. That is a dead giveaway that you are looking at a planet, not a star. Jupiter is famous for its many moons, four of which you can easily see with a small telescope.
Just to Jupiter’s left look for a star, much dimmer than the planet. That is Spica, the brightest star in the constellation Virgo. Our view of the night sky is two-dimensional. Everything up there appears to be the same distance from us. The planets and stars are just too far away from us to be seen in 3D. Right now Jupiter is about 500,000,000 miles distant. Is that a long way? You bet it is! A non-stop Alaska Airlines flight would take about 95 years to take you to Jupiter.
Spica, being a star, is in a whole different zone out there. It lies a whopping 1,500,000,000,000,000 miles away. If you want to take that airline flight there, be ready to take a nice long nap. The journey will take about 300 million years! If Spica is that far away, it must be really bright for us to be able to see it at all. Like many other stars, it is two stars in one and the brightest of the pair shines at over 12,000 times brighter than our puny little sun.
Turn around and look to the east for a large triangle of three bright stars. They are known as the Summer Triangle and will be with us all summer and most of the fall. The star at the top, Vega, and the one on the bottom right, Altair, are close neighbors of ours, right in our cosmic backyard so to speak. The star on the lower left, Deneb, is a far-flung beacon shining at us across a vast gulf of space and time. It is the most-distant single star we can easily see in the night sky. No one is really sure how far away it is or how bright it is. Estimates put it shining at about 200,000 times brighter than our sun.
Look for Saturn
If you can see low in the southeast, maybe you can spot the ringed planet Saturn and the bright star Antares to its right. Saturn is the second-largest planet, and a small telescope will easily reveal its rings and its largest moon Titan.
Why is the sky dark at night? Sounds like a dumb question, doesn’t it? Maybe because the sun is not shining? Actually, this seemingly simple question has bewildered astronomers for centuries. Johannes Kepler, who was the first to plot out the orbits of the planets around the sun, thought about it in the early 1600s. Edmond Halley, discoverer of the famous comet, could not figure it out and even the poet Edgar Allen Poe weighed in on the subject. The question known as Olbers’ Paradox, after a German amateur astronomer, or the dark night sky paradox, has not really been understood until quite recently.
The reasoning goes something like this: If the stars and galaxies go on and on out there, they should blend in together and overlap each other like tree trunks in a great forest. Then all we should be able to see is a blazing light brighter than the sun filling the entire night sky.
The answer lies in our understanding of the universe only realized in modern times. We now know that the universe is huge, maybe even never-ending, but we cannot see the whole thing. We also know that the universe is old, about 14 billion years old, but not infinitely old. The light from the distant galaxies is racing across space towards us at a very fast pace, but not infinitely fast. So the light from the very distant galaxies and stars has simply not had enough time to get to us yet and may actually never get to us. That leaves the dark gaps between the stars that we all see.
So that is why the sky is dark at night, and thank goodness. I have a hard enough time sleeping at night when the days are so long this time of year. It would be a real bother if we never had any darkness at all!
Do you want to see the moons of Jupiter and the rings of Saturn for yourself and you do not have a telescope? Or maybe you are perplexed about this Olbers’ Paradox business and want some clarification. Catch up with me this summer at Sun Mountain Lodge or the Methow Valley Chamber Music Festival and take a look through one of my telescopes. Hope to see you there!